An air intake system of an internal combustion engine known from the market has a first blow-molded duct part made of plastic. A second duct part has a nipple for connection with the first duct part. The nipple of the second duct part is inserted in a connection end of the first duct part. The connection between the first duct part and the second duct part is fixed tightly by welding.
It is an object of the invention to provide a pipe system, a method and an apparatus for connecting at least one duct part of the pipe system of the above-mentioned kind, in which the connection may be realized easily directly inside the mold without external ejection process and the connection is reliable and tight.